Concentric tester



y 1952 c. G. BACON ETAL I 2,604,512

- CONCEN' IRIC TESTER Filed Dec. 6,-1950 8 VE RTI CAL ECCENTRICITY DETECTOR HORIZ ONTAL ,../0 E CCENTRIC [TY OSCILLOSCOPE DETECTOR OSCILLATOR wInventors:

30 ConraclG-Bacon, Paul C. Gardiner.

Their- Attorney.

Patented July 22, 1952 Qb Q IQIE R r p j Conrad G. Baconi l f hiladelphia, Pas and; Paul 0. I Gardiner, Scotia, N. 1L,v assignors to General jElectric Company, a'corpbi'ationof'NewYork Application December 6, 1950,Serial-No. 199,485

ourlinventio n relates to .concentricity testers and more particularlyto devices for checking the concentricity of a conductor with respect.to the insulation therearound. f

v Electric insulation is often'applied to wire by an extrusion typeprocess. Machines, have; been developed to insulate wire by such anextrusion process as the wire is drawn throughthe ma- -'chine. At thepoint-inv such a machinewhere the-extruding process iscompleted and theinsulated wire emerges, .the machine is. provided with adjustable jawsfor regulating the size and shape of the insulated cable. In such aninsulating process the conductor in the insulated cable leaving themachineis xnot always concentric with respect'to the insulation.Departures from the concentric position substantially reduce theinsulation resistance of the'cable 'at the point of departure v At thepresent time the thickness .of -the in,-

' sulation applied to a wire in'an extruding process is madesubstantially greater than.- is necessary in order that minor departuresfrom the concentric position will not violate any predeterminedspecifications for the cable. This type of protection is extremelyexpensive'and is by no means foolproof. In fact, the cable must be cutperiodically to check the concentricity of the conductor with respect-tothe insulation.

Therefore, animportant object of our invention is to provide means fordetecting lack'of concentricity in a cable being delivered from aninsulating machine.

Another object of our inventionis tol'provide means for indicating to anobserver or to a cor- .recting control. device the extent ofrjanyeccentricity of a conductor with respect to the tact with the cable. .Thechanges in capacity between the conductor in the cable and theelectrodes in contact'with the circumference of the cable insulation areused to change the voltages across the outputterminals of capacitivevoltage dividers. The changes in the output voltages of the voltagedividers areamplifiedand applied .toeIectric meters which indicate theposition of the, conductor within, the insulation. I y

1 .The features of our invention which we believe to be novel are setforth with particularity I in the appended claims; Our invention itself,how- :ever, botl as' to;its qrganization.; and method of 1 .operationtogether with further objects and advantages thereof, may bestbeunderstood by ref- .erence. to the following description taken inconnectionwith the accompanying drawing, in which .Fig. l is aconventional box and line diagram of a concentricitytesterembodying ourinvention; Fig. .2-is a schematic circuit diagram of our .iinvention;and-Fig. 3 is a. modification, of the electrode arrangement used in ourinvention.

ductor 2 disposed within the insulation 3.

v;.-R.eferring to the drawings, a cable I has a con- Conductor '2 is tobechecked for concentricity with respect to insulation 3. Conductor 2 isconnected to ground through the insulating machine used to applyinsulation 3 to conductor 2. A plurality of electrodes, such .as theelectrodes 4,15, 6 and 1,

are iii-contact with. insulation 3 and are preferably. spacedat '90 deg;intervals around the circumference thereof. Each of the aforesaidelectrodes effectively forms a variable capacitor with'conductor 2; Asthe position of conductor 2 changes withrespect to insulation 3, thecapac- -itance between conductor 2 and the electrodes also changes. r

Electrodes 4 and 5 are connected to anelectric circuit which we havecalled a vertical eccentricity detector 8; Electrodes 6 and 1 areconnected to a' horizontal eccentricity detector 9.

Detectors 8 and 9 supply to an indicating device v such as theoscilloscope. 10' a signal'which is proportional to the displacement. ofconductor 2 from a concentric position. The output of detector 8'is'connected to the vertical deflection plates of oscilloscope l0, andthe output of deplates of oscilloscope l0.

tector '9 is connected to the horizontal deflection cting cir- Since thevertical and horizontal dete cuits are identical, only' the horizontaldetector circuit 9 is shown in detail. Horizontal detector circuit 9 isshown in detail Fig. 2 in conjunction with a segment of cable I in whichconductor 2 is-displaced from the concentric position. In Fig. 2oscilloscope, II! has been replacedby the zrectifying circuit 2i and.the meter 24.-

The capacitor H is serially connected with the capacitance formed byconductor! andelectrade 6. The capacitor i2 is serially connected withthe capacitance formed by conductor 2' and electrode 1. Each of theaforementioned-series circuits serves as a voltage dividerin detectorcircuit 9 and has one, terminal thereof connected to ground. Anoscillator 13 generating a high iredtibjncy, such as 9.5lkilocycles, isconnected capacitors and is 21c is connectedtogr'ound;

' through onesi'de ofv V I current through the other sideas they aresaid voltage dividers. The output of each of the voltage dividers istaken between ground and the respective electrode. Therefore, whenever Vthe position of conductor 2 changes in a horizontal plane withininsulation 3, the voltage across the output terminals of one of theaforesaid voltage, dividers decreases while the voltage across theoutput terminals of the other voltage divider increases. Statedotherwise, a

.first pair of capacitors comprising the conductor.

2 and the electrodes 6 and 1 respectively is arranged ina bridge circuitwith a second pair of capacitors H and I2. Conductor 2, being grounded,is one input terminal and in reality. constitutes a junction po'nt'between the first" pair of capacitors comprisingcondu'ctor 2 andelectrodes 6 and I. Theiconductor'. connected between capacitors II andI2 to which the os-.

cillator I3 is connected constitutes-a junction point for the capacitorsf the second pair of another input terminal for the-bridg'e 'ci'rcuitiThe-connectionbetween-electrode and capacitor l2; and the connectionbetween electrode iiand ca'pacitorflll constitute a pair of' output Theresistors 14 and I'5 conn'ected from. ground to electrodes 6 and lrespectively'simply serve as grid leak resistors; Resistorslll'and'.:.l5;'are of a relativelyhigh 'magi'litude, *such' .'as." 2Omegohms each. signal maybe derived fr'o'm'the. voltage dividers withoutrequiring an'l extraordinary 'load' of oscillator l3, an impedancetransiormingidevice such as the balanced amplifier" circuit I6 isemployed. Amplifiers I1 and I8 are connected in".

circuit 16- as cathode 'followersa. head. resistors 1 wand 20 areconnected. betweerr ground: and the cathodes ofampli'fiersi Hand'liiirespectively and are of 'a magnitude'suchas 5000'ohms each.

" Electrodes 6" andi'l areconnected'to'thexcontroli: electrodesoffa'niplifiers' lilfand. lBarespectively.

A rectifier;'such.-as the: bridge type rectifier circuit 2|, having:input'terminals. 21a and 2119 and having output terminals 21c and 21d;is connected across the output. terminals; of bale.

anced' amplifiercircuit? l6." Condensers '22; and 23 are blockingcondensers toiprevent thedirect currentcomponenttof:current fiowingiinbalanced I amplifier" circuit. Hi from-2 flowing into; Ibridgerectifier" 2:1; indicatingjdevice: such asthe microammeter; 24; isconnected across the output; terminals-of bridge rectifier 2;l-.Capacitor 25. bypasses the alternating. component ofthe pulsating.direct current flowing from bridge rectifier 2 I around meter- 24.;Meter. 24 ispref erably a direct current microammeter zero; deflectionpoint at mi -scale. Terminal Capacitors 22. and/23' each draw currentbridge rectifier 2 l and drive charged-or dischargedin response toinstantaneous changes in the voltage thereacross; To set up theeccentric indicator circuit for: operation, a section .of cable- Khaving conductor 2 concentric terminalsfor the: bridge circuit;

In: order thatanappreciable having the ance the amplifier circuit l6 andcause meter 24 to show zero deflection.

When conductor 2 is displaced from the concentric position, as shown inFig. 2, the capacity between conductor 2 and electrode 1 is decreasedand the capacity between conductor 2 and electrode 5 is increased. Thisresults in an increase in the potential of] the: control electrode ofamplifier'l8 with respect to ground and a decrease in the potential ofthe control electrode of amplifier I! with respect to ground. Thiscauses amplifier Is to draw considerably more current than amplifier I!with the result that gterminaljla is-raised to a higher potential withrespect to grou nd than terminal 2lb. Current now passes'through meter24 from terminal 2ld togroundonthepositive half cycle of oscillatorvoltage. The deflection on meter 24 is to the right of'mid scale, thusindicating to an observer that conductor 2 has moved to the right. The

f observercan then adjust the jawson the insulating machine tob'ringconductor 2 back into: a

concentric? positionl .LWhen' conductor; 2 .returns to theconcentric-position. the potentials appearing on thecontrolselectrodesiofamplifiers equat and;t-he resnlting'indica- H; and.laibecome "tion' on meter 24'is zero.

' cycle oflthe';

'" onmeter .24: is tothe leit,. thus indicating. to: an

observer that. conductor- Ifconducto'ifZ. moves to the left,

of. detector circuit 9: isisimilarxto that hereinbeiore.described-except that". amplifier ll'now draws considerablymore currentthan amplifier t8 and current is drawn. through meter Mirom ground to..terminal 2 .l d on; the negative half oscillator" voltages. Thedeflection 2: hasimoved to. the; left. Verticaldetector. .81 operatesina: manner similar to that hereinbefore: describedfor. detector 9 toindicate vertical displacement of conductor 2. .When meters are used asindicators,- as in Fig. 2 ;'the operator observes vertical andhorizontal. displacement: of conductor 2'on separate meters..Ifanoscilloscope. is used, as infl ct. 1,

.both displacements .rcan beobservedon the-same screen at the same time.

' ,It has beerrioundthat the-electrodes shownin Figs 1: and12, aresatisfactory for cables having a diametergof 1/ or greater- .However;with smaller 'cablesithe difficulties in constructing electrodesihforsatisfactory, contactwith the insulation become substantial With the,smaller diameter wires an arrangement such as; that shown in Fig. 3 hasbeen found'to beconvenient. In this case,, theelectrodes 1. arecylindrical in J shape, such.- as; the electrodes 26', 21, 28 and;29,

and the cable" passes around. the electrodes.

Thes'eel'ectrodesare mounted on asupportsuch as a Bakelite rod 36:.Cable .L is then. passed around rod 30 as shown in 'Fig 3"so'that-electrodes 26 andfiilbecorheth: electrodesior. de-

and the electrodes detecting tecting horizontal deflection, 2-! and.29': become-the? electrodes for vertical deflection. This-accomplishesengagement of 'thecabl'e with each electrode: fortipand-thatjthos'e'sk'll fi cations inthe proximately' fi de'grees ofthe cable circumference. Thus each electrode sees an: incremental lengthof the cable-insulation involving" degrees circumferentially.-

' r 7 While the preient' invention has been' -'described by reference tothe particular embodiments thereof,'"it '-will be understood that thisisby way of illustration of the principles involved ed in'the'artmaymakemodiangement andi mode? of opascent Therefore" we'contenipiate bytheappended claims to cover any such modifications as fall within the truespirit and scope of our in vention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. For use in conjunction with an insulated conductor, adevice forchecking concentricity of said conductor with respect to the insulationtherearoundand comprising a shaft, cylindrical electrodes mounted onsaid shaft and spaced longitudinally along said shaft, said electrodesbeing concentric with respect to said shaft, said insulated conductorbeing wrapped around said shaft so that said insulation contacts each.of said electrodes substantially in an area 90 degrees displaced fromthe contact area on adjacent electrodes, a difierent eccentricindicating circuit connected to each pair of said electrodes havingdiametrically opposite contact areas, each of said indicating circuitscomprising a bridge-type rectifying device having output and inputterminals, indicating means responsive to current therethrough andconnected across said output terminals, one ofsaid output terminalsbeing connected to ground, a balanced amplifier circuit connected tosaid input terminals, said conductor being connected to ground,

a plurality of capacitors each having one terminal connected to adifferent one of said electrodes, means for producing electricoscillations,

one terminal of said oscillator means connected to the other terminal ofeach of said last-mentioned capacitors, the other terminal of saidoscillator means connected. to ground, and electric circuit meansconnecting said electrodes to .said balanced amplifier circuit.

2. For use in conjunction with an insulated conductor, a device forchecking concentricity of said conductor with respect to the insulationtherearound and comprising a shaft, cylindrical electrodes mounted onsaid shaft and spaced longitudinally therealong, said electrodes beingconcentric with respect to said shaft, said insulated conductor beingWrapped around said shaft so that said insulation contacts a pair ofsaid electrodes, the contact areas of said pair of said electrodes being180 degrees displaced from each other, said pair of said electrodes andsaid conductor constituting a first pair of capacitors, a second pair ofcapacitors, circuit means conmeeting said first and second pairs ofcapacitors in a bridge circuit having input terminals at the junctionpoints between the capacitors of each pair and having output terminalsat the connections between the capacitors of one pair and the capacitorsof the other pair, means for supplying alternating current to said inputterminals, and means responsive to an unbalance of voltage across saidoutput terminals for performing a control or indicating operation.

' CONRAD G. BACON.

PAUL (J. GARDINER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Peters et a1. Mar. 3, 1942

